I have no direct experience with the process, but from what I have read, you need to loosen the engine mounts (only loosen, not remove) and also have an engine hoist capable of lifting the Cummins as high as it can with out hitting the firewall.
At that position the oil pan can be slid out from under the cross member but you still want to be careful not to loosen or bend the oil pickup tube on the way in or out.